By Kim Eun-jung SEOUL, April 10 (Yonhap) -- South Korea and the United States have upgraded their surveillance status on Wednesday to monitor an imminent missile test by North Korea, military officials said, at a time of escalating tension on the Korean Peninsula.

Pyongyang is believed to have completed preparations for a mid-range missile launch from its east coast after it moved two Musudan missiles to its east coast last week by rail and mounted them on mobile launchers.

Ahead of an imminent test, the Combined Forces Command raised "Watchcon" 3 status, a normal defense condition, by one level to step up surveillance monitoring and increase the number of intelligence staff, a senior military official said.

South Korea's military also launched an emergency task force team charged with monitoring and analyzing the latest development in North Korea's preparations, he said.

South Korean and U.S. intelligence officials have been closely monitoring the North Korean facility believed to contain the Musudan missiles mounted on the TELs (transporter-erector-launcher). The missile can fly 3,000-4,000 kilometers, making it capable of hitting the U.S. base in Guam in the Pacific Ocean.

Seoul officials say there are high chances that Pyongyang could fire off a missile around April 15 to mark the birthday of late founding leader Kim Il-sung, the current ruler Kim Jong-un's grandfather. Last year, the North unsuccessfully conducted a rocket launch days before the 100th anniversary of Kim's birth.

Officials in Seoul say there are possibilities that the North may fire off several missiles from different sites, in case of an unsuccessful launch of the Musudan missile, which has never been tested before.

According to satellite imagery, four or five more TELs were recently spotted in South Hamkyung Province, sparking speculation that the North may fire off missiles in several places.

The TELs were believed to be launch platforms for short-range Scud missiles, which have a range of 300-500 kilometers, and medium-range Nodong missiles, which can travel 1,300-1,500 km, the source said.

"There are clear signs that the North could simultaneously fire off Musudan, Scud and Nodong missiles," a government source said, asking for anonymity citing confidential information.

To track the missile's trajectory, two Aegis destroyers with SPY-1 radar, which can track hundreds of targets as far as 1,000 kilometers away, have been on standby on the east and west coasts of the Korean Peninsula.

The South Korean military is also operating the ground-based missile defense radar system Green Pine, and the early warning aircraft Peace Eye under a stepped up military readiness status to prepare for a potential rocket launch, according to military officials.

Japan said Tuesday that it has deployed PAC-3 missile interceptors to key locations around Tokyo.